# Why does alternating current (AC) need a neutral?

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I understand the concept of DC, but if electrons are just kind of moving back and forth in one place to produce an electric charge for AC, why do they say it’s necessary to have a path back to ground/ 0V if it’s not “moving” towards ground/ 0V?

In: 7

The electrons can only really move because the electrons to the front of them move out of the way, and so forth.

Path to and from the source. The source is grounded. The electrons alternate direction but they still move back and forth in the wire. The earth (ground) is a bad wire choice so 2 conductors are used is my understanding.

If you look at electrical current as just a flow of electrons then the electrons still need somewhere to go in the split second it is moving to the load, and they need somewhere to come from in the split second they move from the load. It is hard to actually store large amounts of electrons somewhere as they strongly repel each other. If you put even just one extra electron into a small piece of metal it is going to become negatively charged and the next electron will be repelled by it. So you have to force it inn there which makes it even more negatively charged making it harder to get the next electron into the metal. In the split second the charge of the live wire is negative you will be able to charge a lot of metal to a low enough voltage for the current to stop.

The easiest way to solve the problem of storing the electrons is to send it back through the neutral line to the transformer. In the most common grid systems there is not really any current going to ground, it is all going back to the transformer. There are however a few systems which do use the ground as a return instead of the neutral wire. In these systems the ground is basically used as a huge piece of conductive material where the electrons can be stored for later use without charging it much. I think this is limited to a few rural Australian systems and some older electrified rail systems. But in higher frequency applications this is far more common. For example a lot of radio antennas use the ground in this way, or even the other half of the antenna. And a Tesla coil uses the air to hold charge for a tiny fraction of a microsecond.

Think of a water pipe in wich a piston moves the water forwards and backwards (alternating current).
If the system is closed the water would splash around in the area of the piston.

But if you make a loop of pipes from one side of the piston to the other, the entire water in the loop would move back and forth (ignoring friction/inertia for simplicity)

Now you could put a water wheel inside the pipe with would get pushed forwards and backwards and you can do work with that, grind some flour or something.

That’s the concept of alternating current, piston is the generator, water the electrical current, the water wheel is a motor.

The concept of electricity flowing from one point to another is physically wrong but the simplest way to understand it without deeper knowledge

To control where the electrons flow. Without the path back, the electrons will look for a high conductive path to a lower potential, which likely doesn’t exist naturally in the environment in a way that serves the purpose of what you are trying to power.

Just like hanging a swing from a bar with a chain allows the swing to go back and forth through an intentional low point, rather than have you crash into the ground or get stuck in a tree branch.